Electronic device for measuring statistical parameters of stochastical processes

ABSTRACT

An electronic device for measuring statistical parameters of a stochastical process represented by an electrical signal which is sampled by a clock frequency, the sampled values being divided into at least two classes of sizes by comparison with at least one controllable threshold voltage, and statistical parameters of the stochastical process measured, comprising at least one controllable sampled amplitude discriminator the input of which is connected to the electronic source of said signal and an automatic device having at least one set of bistable elements and at least one set of electronic means for controlling the sampled amplitude discriminator.

324-077.- OR 3568055 SR United SlfltES Patent 3,568,055

Invent Wolfgang welfmann [56] References Cited [211 App] No z'f g sUNITED STATES PATENTS [221 Filed (M11967 2,779,869 1/1957 Gerks324/77(A)X [45] Patented Mar. 2,197] 2,820,896 1/1958 Russell et al.....324/77(A)UX [73] Assignee Norma Fabrik dektrischer Messgel-age 3,023,9663/1962 Cox et al 324/77(H)UX Gesellschatt m.b.H. 3,125,721 3/1964Schumann... 324/77(A)X Vienna, Austria 3,422,349 1/1969 Makino 324/77(A)[32] Priority Oct. 6, 1966 FOREIGN PATENTS Austria 1,175,470 8/1964Germany 324/7701) [31] 9356/66 Primary Examiner-Edward E. KubasiewlczAttorney- Holman, Glascock, Downing and Seebold ABSTRACT: An electronicdevice for measuring statistical parameters of a stochastical processrepresented by an electri- [54] ggg g cal signal which is sampled by aclock frequency, the sampled PROCESSES values being divided into atleast two classes of sizes by comshims 1o Drawin H s. parison with atleast one controllable threshold voltage, and g g statistical parametersof the stochastical process measured, [52] US. Cl 324/77, comprising atleast one controllablesampled amplitude dis- 328/117 criminator theinput of which is connected to the electronic [51] Int. Cl G0lr 23/16source of said signal and an automatic device having at least [50] Fieldof Search ..324/77 (A); one set of bistable elements and at least oneset of electronic 1 Gen.

means for controlling the sampled amplitude discriminator.

4- -8, eisne e I use: s f--;a,, 1" DISCRIMINATOR L J POTENTIOMETER 5 '0ELECTRONIC DEVICE FOR MEASURING STATISTICAL PARAMETERS OF STOCHASTICALPROCESSES The present invention relates to an electronic device formeasuring statistical parameters of a stochastical process the values ofwhich being represented by an electrical signal which is sampled by aclock frequency, the sampled values being divided into at least twoclasses of sizes of amplitudes by comparison with at least onecontrollable DC level (threshold voltage), and statistical parameters ofthe classes, for example total, joint and conditional probabilities orcorrelation functions and spectra, respectively, are measured. Theelectrical signal represents a stochastical process which is alreadyelectronically generated or, by means of a transducer, in said signaltransduced.

Devices for classification of stochastical processes are known, somehave mechanical, some electromechanical construction (for instance:Austrian Pat. Nos. 175, 084; 202, 385; 203, 247; 206, 677). Also knownare machines for determination the relative frequency of randomevents'(for instance: relative frequency counter 4420 of Bruel & Kjaer,Denmark). The disadvantages of said known devices and other well knownprocedures for classification or measuring statistical parameters ofstochastical processes are that only the total probabilities of onlyslowly fluctuating processes can be measured and any variation of theclass sizes is very complicated,

which variation requires, forinstance the changing of mechanicalcomponents of said devices. 1

An object of this invention is toachieve the measuring of probabilitiesin a new and very profitable advantageous manner with respect to priorart, especially to provide an amplitude distribution measuring system inwhich the sizes of the classes of amplitude can be easily andcontinuously varied, the variation being performed either manually orunder the control of an electrical signal, for measuring statisticalparameters of at least one stochastical process. It is a further objectof the invention to provide an electronic device which is applicablewhen the concerned stochastical process has high frequency components,too.

Another object of the invention is to provide an electronic deviceadapted to control each class volume in dependence of an own or the samestochastical process, eventually processed by communication systems, formeasuring correlation functions and spectra of these stochasticalprocesses. I

With this objects in view the invention provides an electronic devicecomprising in combination'at least one controllable sampled amplitudediscriminator the input of which is connected to the electronic sourceof the electrical signal representing the stochastical process, and anautomatic device with at least one set of bistable elements storing thestates of the automatic device, said set having at least one bistableelement being connected to a gate, with at least one set of electronicmeans having outputs controlling the sampled amplitude discriminatoreventually in dependence of the momentary states of the automaticdevice, and with outputs delivering the output voltages which correspondto the states of the automatic device and are obtained for measuringstatistical parameters of the stochastical process.

Further objects, features and advantages of the invention will be moreapparent from the following description taken in connection with theaccompanying drawing, wherein:

FIG. 1 is a block diagram of one embodiment of the present invention;

FIG. 2 shows the signal processing in the sampled amplitudediscriminator;

FIG. 3 shows details of the logical network;

FIG. 4 shows details of the automatic device;

FIG. 5 and FIG. 6, respectively, show particular sets of the bistableelements for measuring the joint and conditional probabilities,respectively;

FIG. 7 is an arrangement of the electronic components for controllingthe sampled amplitude discriminator;

FIG. 8 is a modified electronic device for measuring statisticalparameters of stochastical processes which are mixed with other signals;

FIG. 9 is a diagrammatic view of a stochastical process mixed with astep function; and

FIG. 10 shows a block diagram of an electronic device for measuringcorrelation functions and spectra.

A sampled amplitude discriminator 7 of FIG. 1 classifies the sampledamplitudes of the stochastical process into three cl sses. A signalsource 1 generates a stochastical process s(r) with an additive DClevel, so that the sampled amplitudes have only one polarity. A scanner2 transduces the stochastical process into an amplitude modulated pulse.The scanner 2 is connected to an adjustable clock frequency generator 3.The output of the scanner 2 is connected to decision networks 4a and 4bwhich are fed with the amplitude modulated pulse and decide whether thepulse amplitudes are greater or less than the threshold voltages U, andU,,,, respectively.

Such a decision procedure is explained in detail in FIG. 2. Thestochastical process s(r) with additive DC level is shown in FIG. 2a andthe derived amplitude modulated pulse in FIG. 2b. The sampled values s(tare compared with a threshold voltage for instance U It is evident thatan unipolar amplitude modulated pulse simplifies the comparisonprocedure. If the value s( t is greater than U then at the output of thedecision network 4a the event X occurs as an impulse, else as no impulse(FIG. 2c). The sequential occurence of the events X is a binary randomsequence. The decision network 4b works quite similarly and generates abinary random sequence Y.

The outputs X Y of the decision networks 40 and 4b are connected to alogical network 6 having "gates 6a and 6b (FIG. 3). Said network 6 isfed with the binary random sequences X and Y (FIGS. 1 and 3) andgenerates three new binary random impulse sequences Z Z Z which areobtained at the outputs A A A of the logical network 6. For explainingthe logical structure of the logical network 6 it is useful to define anequivalence between the event impulse or no-impulse, respectively, and alogical ONE. or ZERO, respectively. 7

The outputs A A and A of the logical network 6 (FIGS. 1 and 3) areconnected to an automatic device 8 shown in FIGS. 1 and 4 and having aset of electronic means 5 for controlling the sampled amplitudediscriminator 7. The electronic means 5 comprises two potentiometers 5aand 5b. According to FIG. 4 potentiometer 5a is connected between theslider and the grounded terminal of potentiometer 5b so that therelation holds, and the occurence of an impulse in the sequence Yimplies an impulse in the sequence X, so that the following threedifferent cases of the joint event (X, Y) can be distinguished:

l. X 0, Y= 0 is equivalent to the relation 03 I s(t,,.) I s U whichdetermines the first class of amplitude vaues 2. X l, Y= 0 is equivalentto the relation U fi |s( t I s U,,,, which determines the second classof amphfiide values 3. X l Y= l is equivalent to the relation U,,,Sls(t,,-l 5 U, which determines the third class of ampFtude values Othercases of the joint event (X, Y) are impossible. FIG. 3 makes clear thateach of these cases implies an impulse at the respective output of thelogical network 6. The respective equivalent relations define thecorresponding classes of amplitude values and dependence of the classvolumes related to the threshold voltages U and U,,,, respectively. Thethree random sequences Z Z Z correspond to the three classes ofamplitude values and control the automatic device 8.

The automatic device 8 shown in FIG. 4 has a set 5 of electronic meanscontrolling the sampled amplitude discriminator and a set 10 of bistableelements. The set 10 comprises a set 9 of units 9 wherein i,j= l, 2, 3,and a set 11 of flip-flops 11, (i l, 2, 3). As shown in FIG. 4 eachflip-flop 11, has an input E, connected to the corresponding output A,of the logical network 6 (FIG. 1) and an input connected to theadjustable clock frequency generator 3. As shown in FIG. 5 each unit 9,,

comprises a flip-flop 13, an AND-gate 14 and a delay circuit 15, theinputs of the flip-flop being connected to the AND- gate and to theadjustable clock frequency generator 3, respectively. The automaticdevice 8 delivers output voltages for measuring statistical parametersof the stochastical process s(t). In the following paragraphs theprocedure of measuring the total, joint and conditional probabilitieswill be explained.

Connecting the output A (j =1, 2, 3), of the electronic device 6 of FIG.1 with the input E, of a flip-flop 11, which is set by an impulse at theinput E, and reset if there is no impulse at the input E the timeaverage of the output voltage of the flip-flop being directlyproportional to the total probability p(j), where p(i) denotes theprobability that an amplitude value belongs to the class K}, and isindicated by means of a moving-coil instrument at the output B The totalprobability also may be measured by a digital counter if the externaltime base input of the counter is fed with the clock frequency and thesignal input of the counter is connected to the output By. For measuringthe joint probability p(i, j) which denotes the probability thatfollowing amplitudes belong to the classes K, and K,, (i,j= l, 2, 3) aflip-flop l3 ofunit 9 (FIGS. 4, is set if an impulse at E, immediatelyfollows an impulse at E,, else the flip-flop is reset (FIG. 5). For thisreason, the impulse at E, is delayed by means of the delay circuitconnected to the first input of the AND-gate 14, the second input ofsaid AND- gate receiving the impulse at E, The time average of theoutput voltage of the flip-flop 13 is directly proportional to the jointprobability p(i, j) and may be measured by means of a moving-coilinstrument 16 at the output B The digital measurement of the jointprobability is quite similar to the measurement of the totalprobability. Three and more dimensional joint probabilities can bemeasured quite analogous if at coincidence of three or more respectivedelayed impulses at the corresponding outputs of the sampled amplitudediscriminator 7 of FIG. 1 a flip-flop is set, else the flip-flop reset.The time average of the output voltage of the flip-flop is directlyproportional to the more dimensional joint probability and may be readout analogue or digital.

The conditional probability p(j/i) denotes the probability that anamplitude value belongs to the class K 1 upon the condition that thelatest amplitude value belonged to the class l(,, and is digitallymeasured best. For this purpose in a set 10' of bistable elements shownin FIG. 6 a flip-flop I is set if an impulse appears at the input 15,,else the flip-flop I is reset. A flipflop II is set if an impulse at theinput E, coincides with the respective delayed impulse at the input E,,the impulse at E, being delayed by means of a delay circuit 17 and thecoincidence being proved by an AND-gate 18 connected to the delaycircuit and the input E Further, the flip-flops I and II are connectedto the adjustable clock frequency generator 3. Connecting the output offlip-flop I with an external time base input of a digital counter 19,and connecting the output of flipflop II with its signal input, thecounter indicates the conditional probability p(j/i) (FIG. 6).

The application of the invention to the measuring of probabilities canbe enlarged if the condition U U,,, A U. =constant holds for allvariations of the threshold voltages U and U. By this way it is possibleto move the voltage interval A U, over the whole amplitude field of thestochastical process and to measure the probability that an amplitude ofthe stochastical process belongs to this interval. This method has thesame effect as an electronic device according to FIG. I for equidistantclasses, with U, {I s(t) I} Mr, For this purpose the potentiometer set 5in FIG. 1 is replaced by a set 5' (FIG. 7) which consists of tworesistors 50' and 5b simultaneously variable in opposite sense which areconnected in series with an adjustable resistor 5c lying between themfrom ends of which the threshold voltages are picked up. The voltagedifference A U, is varied by the resistor 50'. Simultaneous andoppositely directed variation of the resistors 5a and 5b moves thevoltage interval A U over the whole amplitude field of the stochasticalprocess.

The combination of more sampled amplitude discriminators according toFIG. 1, which are controlled by the same clock frequency but fed withdifferent stochastical processes, with an automatic device 8 accordingto FIG. 1 allows the measurement of statistical parameters which definethe statistical relations between the different stochastical processes.The procedure of measurement is quite similar to the proceduresdescribed above. For example the joint probability p(t", 1"") whichdenotes the probability that an impulse at the output A of the sampledamplitude discriminator I appears simultaneously with an impulse at theoutput A," of the sampled amplitude discriminator II, is measured bysetting a flip-flop if an impulse at A, coincides with an impulse at A,and by indicating the time average of the output voltage of the flipflopby a moving-coil instrument or a digital counter.

FIG. 8 shows a modification of the electronic device according to FIG. 1for measuring statistical parameters of a stochastical process s(t)which is mixed with a signal r(t) for instance with a step functionhaving three amplitude steps (FIG. 9). The classification of thestochastical process in the described manner is possible if thethreshold voltages of the sampled amplitude discriminator 7a aregradually controlled corresponding to the step function. The sampledamplitude discriminator 7b determines the momentary amplitude step ofthe step function and controls the threshold voltages of the sampledamplitude discriminator 7a in dependence of this step. For this purposethe automatic device 8' of FIG. 8 comprises a set 11 of bistableelements according to FIG. 1 which stores the decision of the sampledamplitude discriminator 7b and changes the adjustable threshold voltagesof the sampled amplitude discriminator 7a. If an impulse is obtained atthe output S, of the set 11 the threshold voltages of the amplitudediscriminator 7a are changed by closing the switches s s i, s,', (i 1,2, 3). By this procedure one of three potentiometer sets 12a, 12b, 12cis selected and delivers the threshold voltages for the amplitudediscriminator 7a. The set of bistable elements 10 is the same as in FIG.1 and serves for measuring the relative frequency of the automaticdevice states in the above described manner. This method may besimplified if also r( t) is available. In this case the electronicdevice of FIG. 1 is used and the potentiometer set 5 is supplied withthe voltage U, r(t). At the outputs of the automatic device voltages formeasuring statistical parameters of the stochastical process s(t) areobtained.

The electronic device of FIGS. 1 and 8 may be extended for any moreclasses where for n classes the sampled amplitude discriminator needs(n 1) binary decisions networks and threshold voltages, the logicalnetwork comprises (n l) AND-gates, and the automatic device has at leastn bistable elements.

' The correlation functions and spectra may be determined by the sameprocedure as for measuring total probabilities (FIG. 10). For thispurpose two sampled amplitude discriminators 21 and 22 are provided,each one fed with an evenly distributed stochastical process which isstatistically independent from the other stochastical process, whichprocesses by example are delivered from noise generators 23 and 24,respectively. The amplitude discriminators 21, 22 are sampled by meansof a clock pulse generator 25 (FIG. 10). The sampled amplitudediscriminator 21 is controlled by a threshold voltage which is directlyproportional to a signal s (t produced by an electronic means 26, e.g. asignal generator, the other sampled amplitude discriminator 22 iscontrolled by a threshold voltage which is directly proportional to thedelayed signal s,(t t,). Said delayed signal is produced undelayed bythe electronic means 26 and becomes delayed by means of a delay circuit27 interconnected between said electronic means and the amplitudediscriminator 22. The output sequences of the two sampled amplitudediscriminators 21, 22 are logically configurated by an AND-gate 28 whichis provided in an automatic device 29 having a flip-flop 30. The inputsof said flip-flop 30 are connected to the AND-gate 28 and to the clockpulse generator 25, respectively. The output of said flip-flop 30 isconnected to a moving-coil instrument 31. The average of the totalprobability for an impulse in the output sequence of the AND-gate 28 isdirectly proportional to the correlation function of s,(t) for the delayargument t and may be read out in analogue or digital manner. If thesampled amplitude discriminators 21, 22 are controlled by a thresholdvoltage, which is directly proportional to the amplitude of thefrequency component (a, of s 0) which may be obtained by respectivefiltering of s 0), the average of the total probability 'for an impulsein the output sequence of the AND-gate 28 is directly proportional tothe power density spectrum of s,(t)

for the frequency component 0);. By using more, for instance m, sampledamplitude discriminators in analogous manner the correlation functionsand spectra of (m 1) order may be measured. a

lclaim:

1. In an electronic device for measuring statistical parameters of astochastical process the values of which being represented by anelectrical signal which is sampled by a clock frequency, the sampledvalues being divided into at least two classes of sizes of amplitudes bycomparison with at least one controllable direct current level(threshold voltage), and statistical parameters of the stochasticalprocess being measured, the improvement comprising'in combination atleast one controllable sampled amplitude discriminator having an inputand at least one decision network, which input is connected to theelectronic source of the electrical signal representing the stochasticalprocess and which decision network dividing said sampled values intosaid classes by comparison with said direct current level, and anautomatic device having at least one set of bistable elements definingand storing operating states of the automatic device, said set having atleast one gate with an output and at least one bistable element havingan input being connected to said output of said gate, at least one setof electronic means having outputs controlling the sampled amplitudediscriminator, and outputs delivering output voltages which outputvoltages correspond to the states of the automatic device and whichoutput voltages are obtained for measuring statistical parameters of thestochastical process.

2. An electronic device according to claim 1 wherein the set ofelectronic means controlling the sampled amplitude discriminator has aninput connected to voltages corresponding to the momentary states of theautomatic device.

3. An electronic device according to claim 1 wherein thebistableelements of the automatic device are flip-flops and theelectronic means for controlling the amplitude discriminators are directcurrent supplied potentiometers.

4. An electronic device according to claim. 2 wherein the bistableelements of the automatic device are flip-flops and the electronic meansfor controlling the amplitude discriminators are direct current suppliedpotentiometers.

5. An electronic device according to claim 3, comprising a signal sourcedelivering a signal which is independent of the stochastical processwherein the inputs of the flip-flops are connected to said signalsource.

6. An electronic device according to claim 1 having a signal generatordelivering a signal which is independent of the stochastical processwherein at least one. of said sets of electronic means controlling thesampled amplitude discriminators is connected to said signal generator.

7. An electronic device according to claim 2 wherein said automaticdevice has a set of switches switched in dependence of the momentarystate of the automatic device and a plurality .of sets of electronicmeans for controlling the sampled amprocedure.

9. An electronic device according to claim 8 wherein the potentiometersconsist of two variable resistors which are connected in series with anadjustable resistor having two ends lying between them, each of thevariable resistors having a slider connected to the adjacent end of saidadjustable resistor, said sliders being coupled together and each of theends of said adjustable resistor being connected to one sampledamplitude discriminator.

10. An electronic device according to claim 1 wherein said at least onediscriminator comprises a first and a second controllable sampledamplitude discriminator the inputs of which are connected to theelectronic source of the electrical signal representing the stochasticalprocess and an additional signal representing a step function and saidautomatic device has a first and a second set of bistable elements and afirst and a second set of electronic means, the said first set ofelectronic means controlling said second sampled amplitudediscriminator, and the said second set of electronic means controllingsaid first sampled amplitude discriminator.

l 1. An electronic device according to claim 1 wherein said at least onediscriminator comprises a first and a second sampled amplitudediscriminator, the input of the first discriminator being fed with avoltage representing a stochastical process and with an additionalsignal and the input of the second sampled amplitude discriminator beingfed with said additional signal voltage, and the automatic device has atleast a first set of bistable elements and a first and a second set ofelectronic means, the said first set of electronic means controllingsaid second sampled amplitude discriminator, and vice versa.

12. An electronic device according to claim 1 comprising at least twocontrollable sampled amplitude discriminators, the input of each onebeing connected to a separate electronic source which sources deliverelectrical signals representing at least two different stochasticalprocesses.

13. An electronic device according to claim 1 comprising stochasticalgenerators each of which has an output delivering a separate evenlydistributed stochastical process and one signal generator having anoutput, the input of each controllable sampled amplitude discriminatorbeing connected to an output of one of said stochastical generators, andall of said amplitude discriminators having control inputs connected tothe output of said only one signal generator delivering the signal whichis independent of the input signals of said amplitude discriminators.

14. An electronic device according .to claim 1 comprising stochasticalgenerators each of which has anoutput delivering a separate evenlydistributed stochastiealprocess and signal generators having outputs,the input of each controllable sampled amplitude discriminator beingconnected to an output of one of said stochastical generators, and eachof said amplitude discriminators having control inputs connected to theoutput of one of said signal generators which output delivers a signalwhich is independent of the input signals of said amplitudedisc'riminators.

1. In an electronic device for measuring statistical parameters of astochastical process the values of which being represented by anelectrical signal which is sampled by a clock frequency, the sampledvalues being divided into at least two classes of sizes of amplitudes bycomparison with at least one controllable direct current level(threshold voltage), and statistical parameters of the stochasticalprocess being measured, the improvement comprising in combination atleast one controllable sampled amplitude discriminator having an inputand at least one decision network, which input is connected to theelectronic source of the electrical signal representing the stochasticalprocess and which decision network dividing said sampled values intosaid classes by comparison with said direct current level, and anautomatic device having at least one set of bistable elements definingand storing operating states of the automatic device, said set having atleast one gate with an output and at least one bistable element havingan input being connected to said output of said gate, at least one setof electronic means having outputs controlling the sampled amplitudediscriminator, and outputs delivering output voltages which outputvoltages correspond to the states of the automatic device and whichoutput voltages are obtained for measuring statistical parameters of thestochastical process.
 2. An electronic device according to claim 1wherein the set of electronic means controlling the sampled amplitudediscriminator has an input connected to voltages corresponding to themomentary states of the automatic device.
 3. An electronic deviceaccording to claim 1 wherein the bistable elements of the automaticdevice are flip-flops and the electronic means for controlling theamplitude discriminators are direct current supplied potentiometers. 4.An electronic device according to claim 2 wherein the bistable elementsof the automatic device are flip-flops and the electronic means forcontrolling the amplitude discriminators are direct current suppliedpotentiometers.
 5. An electronic device according to claim 3, comprisinga signal source delivering a signal which is independent of thestochastical process wherein the inputs of the flip-flops are connectedto said signal source.
 6. An electronic device according to claim 1having a signal generator delivering a signal which is independent ofthe stochastical process wherein at least one of said sets of electronicmeans controlling the sampled amplitude discriminators is connected tosaid signal generator.
 7. An electronic device according to claim 2wherein said automatic device has a set of switches switched independence of the momentary state of the automatic device and aplurality of sets of electronic means for controlling the sampledamplitude discriminators, said set of switches connecting one of saidsets of electronic means to one of said sampled amplitudediscriminators.
 8. An electronic device according to claim 3 whereinsaid potentiometers provided in the automatic device are connected to aconstant direct current voltage during a measuring procedure.
 9. Anelectronic device according to claim 8 wherein the potentiometersconsist of two vaRiable resistors which are connected in series with anadjustable resistor having two ends lying between them, each of thevariable resistors having a slider connected to the adjacent end of saidadjustable resistor, said sliders being coupled together and each of theends of said adjustable resistor being connected to one sampledamplitude discriminator.
 10. An electronic device according to claim 1wherein said at least one discriminator comprises a first and a secondcontrollable sampled amplitude discriminator the inputs of which areconnected to the electronic source of the electrical signal representingthe stochastical process and an additional signal representing a stepfunction and said automatic device has a first and a second set ofbistable elements and a first and a second set of electronic means, thesaid first set of electronic means controlling said second sampledamplitude discriminator, and the said second set of electronic meanscontrolling said first sampled amplitude discriminator.
 11. Anelectronic device according to claim 1 wherein said at least onediscriminator comprises a first and a second sampled amplitudediscriminator, the input of the first discriminator being fed with avoltage representing a stochastical process and with an additionalsignal and the input of the second sampled amplitude discriminator beingfed with said additional signal voltage, and the automatic device has atleast a first set of bistable elements and a first and a second set ofelectronic means, the said first set of electronic means controllingsaid second sampled amplitude discriminator, and vice versa.
 12. Anelectronic device according to claim 1 comprising at least twocontrollable sampled amplitude discriminators, the input of each onebeing connected to a separate electronic source which sources deliverelectrical signals representing at least two different stochasticalprocesses.
 13. An electronic device according to claim 1 comprisingstochastical generators each of which has an output delivering aseparate evenly distributed stochastical process and one signalgenerator having an output, the input of each controllable sampledamplitude discriminator being connected to an output of one of saidstochastical generators, and all of said amplitude discriminators havingcontrol inputs connected to the output of said only one signal generatordelivering the signal which is independent of the input signals of saidamplitude discriminators.
 14. An electronic device according to claim 1comprising stochastical generators each of which has an outputdelivering a separate evenly distributed stochastical process and signalgenerators having outputs, the input of each controllable sampledamplitude discriminator being connected to an output of one of saidstochastical generators, and each of said amplitude discriminatorshaving control inputs connected to the output of one of said signalgenerators which output delivers a signal which is independent of theinput signals of said amplitude discriminators.